PRXV was secreted into the medium by the epithelial cells. Cell-conditioned medium from different cell cultures (A549, Calu-3, RAW264.7, THP-1) without FCS was analyzed by Western blot analyses for the presence of PRXV. Recombinant PRXV was used as the control. In the medium conditioned by the A549 cells, only a high molecular-weight form of PRXV (either polymer or possibly a glycosylated form) was present. The RAW 264.7 cells did not show appreciable amounts of PRXV secretion. B: Upon stimulation with PAO1 without FCS, secretion of PRXV into the medium by the A549 or RAW 264. 7 cells showed no change. Western blot analyses of cell-conditioned medium (without FCS) upon stimulation with PAO1. Western blot analyses of the medium with FCS provided substantial non-specific staining, precluding illustration.